In addition to various kinds of timepieces used as wristwatches, such as an analog timepiece displaying time by hands and a digital timepiece displaying time on a liquid crystal device, there has recently been developed a two-layer display type of timepiece in which a liquid crystal panel is superimposed on the surface of an analog timepiece, as disclosed in, for example, Japanese Patent Publication No. 59-32755. With such a two-layer display type of timepiece, a digital time display can be superimposed on top of an analog time display, to make it visible.
In the prior art, the display of a liquid crystal panel is often of a color that has a low brightness, such as black, which means that the display of the liquid crystal panel cannot be clearly seen if the analog dial plate is not of a color that has a high level of brightness, such as white. This limits the design of such a dial plate.
That is why a display element having a polymer dispersed liquid crystal layer has been developed, as disclosed in International Publication No. WO94/23331. This liquid crystal layer has the property of being transparent when no electrical field is applied thereto, but it diffuses or scatters light when an electrical field is applied. Therefore, a light-scattering region to which an electrical field has been applied appears to be white or gray, making it possible to display characters or the like. Since the color of this display portion is white or gray, that in itself is novel, and it means that the dial plate can be given a color of a low level of brightness, such as black, blue, or red, and thus the dial plate can be freely designed.
In this case, light is scattered both forward and backward with respect to the direction in which the light is incident, within a region of the polymer dispersed liquid crystal layer to which the electrical current is applied. When a transmissive type of liquid crystal panel has been fabricated by using this polymer dispersed liquid crystal layer, light that is scattered forward in the direction in which light is incident (hereinafter called "forward-scattered light") strikes the eyes of the observer, so this forward-scattered light can be used to provide a liquid crystal display that is white or gray.
A wristwatch or the like is required to be compact, lightweight, and energy-thrifty, so it is often inevitable that a reflective liquid crystal panel is used therefor. In such a case, light that is scattered backward with respect to the light-incident direction (hereinafter called "backward-scattered light") strikes the eyes of the observer. On the other hand, forward-scattered light is directed along the direction in which light is incident, so it does not strike the eyes of the observer.
Research performed by the present inventors has shown that, when a reflective liquid crystal panel has been constructed by using a polymer dispersed liquid crystal layer, there is insufficient backward-scattered light, so that it is not possible to provide a suitable liquid crystal display in white or gray if the forward-scattered light is not reflected. They have determined that this is particularly obvious when the quantity of backward-scattered light is greater than the quantity of forward-scattered light.
In this two-layer display type of timepiece, a member capable of reflecting the forward-scattered light is simply the dial plate, which is disposed forward of the liquid crystal panel in the direction in which light is incident. However, if this dial plate has a low level of brightness, insufficient light is reflected from the dial plate, and thus the display on the liquid crystal layer can not be seen. To counter this, there is no option but to make the dial plate a reflective surface, but this has the effect of further limiting the design of the dial plate.
When a structure is used that causes the forward-scattered light to be reflected outside of the liquid crystal panel, the forward-scattered light diffuses within the space between the liquid crystal panel and the dial plate, generating a loss of light reflected off the dial plate and returning towards the front side.
Furthermore, if forward-scattered light is reflected at a location far from the liquid crystal layer that generates the backward-scattered light, and if the line of sight of the viewer is at an angle to the perpendicular of the liquid crystal panel, there is a danger that a duplicated display will be caused by the pattern formed by backward scattering and the pattern formed by forward scattering.
Such problems are not limited to a two-layer display type of timepiece; they form a common subject of technical concern in the design of other types of electronic equipment in which a background display portion is provided behind a liquid crystal layer.